Self-excited synchronous machine



Nav. 2, 1943.

R. c. ROBINSON 2,333,582 SELF-EXCITED SYNCHRONOUS MACHINE Original Filed Sept. 5, 1939 INVENTOR Hubert CFObiHSOH.

ATTORNEY Patented Nov. 2, 1943 SELF-EXCITED SYNCHRONOUS MACHINE Robert C. Robinson, Wilkinsburg, Pa., assignor to Westinghouse Electric 8,; Manufacturing C'ompany,,East Pittsburgh, Pa., a corporation of Pennsylvania Substituted for application Serial No. 293,368, September 5, 1939. This application December 9, 1941, Serial No. 422,198

Claims.

This application is a substitute for my application, Serial No. 293,368, filed September 5, 1939.

My invention relates to self-excited synchronous machines, and it has particular relation to improvements in synchronous motors, whereby lower manufacturing-costs are obtained, together with improved operating-characteristics and performance.

At present, the most important object of my invention is believed to be the provision of a polyphase synchronous motor, with the exciting winding placed on laminated salient-poles, and with a commutator, instead of slip rings, and with a plurality of leads brought out from intermediate points in each of the field-windings, on the respective salient poles, and brought out to successive commutator-segments, and with three brushes (or polyphase brushes) bearing on the commutator and supplied with three-phase (or polyphase) current in series-circuit relation to the three-phase armature-winding of the motor. The result of such a construction is a substantially non-pulsating unidirectional flux in the field-core, with alternately north and south poles, at synchronous speed; and since the flux does not change, as the successive commutator-segments move under the brushes, the mutual inductance of the concentric coils or part-winding sections of the field-winding removes one of the greatest commutation-difficulties, namely the voltage due to changing flux-interlinkages in the coils undergoing commutation.

It will thu be seen that I achieve a reduction in the cost of the motor, because I have no damper winding, no exciter, and no control-apparatus such as direct-current relays, panelboards or resistances, which is more than offset against a slightly increased cost of the field-winding due to the intermediate taps, and the slightly greater cost of the commutator a compared to sliprings. At the same time, I reduce the spacerequirements, because of the omission of the exciter and the resistors, control-apparatus, and control-panel. I also obtain better efiiciency, because of the elimination of the power which was previously required by the direct-current exciter.

At the same time, my improved motor is selfstarting, operating, during the starting-period, in a. manner somewhat similar or analogous to a polyphase commutator motor, with the important distinction that my motor has its commutated rotor-winding in the form of concentric coils for each pole, so that flux can be produced only in a predetermined magnetizing axis, as distinguished from the distributed windings,

and rotating fluxes, which are produced in the rotor of an ordinary polyphase commutator motor. It is the concentric-coil construction which fixes the flux-axis in the field-member or rotor of my motor, and which causes my motor to have a very pronounced synchronizing torque, causing it to fall into synchronism, and operate at synchronism, without speeding up to over-synchronous speeds as in the ordinary polyphase commutator motor. I

It will thu be seen that the functional operation of my improved synchronous motor involves many important advantages. The operation is simplicity itself: The simple closing of a lineswitch or breaker causes the motor to start, and to run up to synchronous speed, and to fall into step without any further attention, the motor requiring no synchronizing, and no angleswitching. My motor has no current-surge, on synchronizing. It has a very good startingtorque, with an extremely low current-inrush at startingvery considerably better than the ordinary synchronous motor in this regardbecause my commutator-connected field-winding, which offer only a slight inductance, due to leakage, during the non-pulsating flux-conditions of synchronous operation, ofiers a very considerable inductance during starting, thus pulling down the starting-current inrush, while the very superior starting-torque characteristics of a polyphase commutator motor gives my motor a good starting-torque, even at this reduced current-inrush. My motor has high pull-in and pull-out torques, especially with series excitation. With the series excitation, that is, with the polyphase brushes connected in series-circuit relation to the armature-winding, my motor can be adjusted or designed to give an approximately constant power factor, or approximately constant wattless kva,

under varying load-conditions, or it can be ad-- justed to have any other desired wattless characteristic.

In its more general aspects, my invention is not limited to motors, being applicable also to, generators; and it is applicable to single-phase apparatus illustrating my invention as embodied in a serially-excited three-phase motor,

Fig. 2 is a somewhat simplified diagrammatic view illustrating the application of my invention to a shunt-excitedself-excited motor,

Fig. 3 is a similar simplified diagrammatic view of a single-phase motor embodying my invention; and

Fig. 4 is a longitudinal sectional view illustrating the physical construction of a motor, of;

the type shown in Fig. 1.

In Figs. 1 and 4, I have illustrated my invention as comprising a three-phase armature-v Will be an even number of salient poles H, to-

provide alternatingly north and south poles, as is usual in synchronous-motor construction.

a plurality of polar coils wound on the respective salient pole-pieces H in a manner similar to an ordinary synchronous motor, except that, in accordance with my-invention, each pole ofthe field-winding 2B is provided with a plurality of intermediate electrical tap-connections which divide each pole-piece winding into a plurality of serially connected coils or part-winding sections 22 between these tap-connections 2|.

The poles of the field winding 20, in the'particular machine which I have chosen for illustration, are connected in series, in a continuous circuit as indicated by the intermediate serial connections 23. and 24 (Fig. 1), in such polarity that .one pole of each pair of poles has one polar ity, while the otherpole has the other polarity,

so that the.machine.has alternately north .and south poles,v during synchronous operation, as in ordinary synchronous machines.

,It will be noted that the coils 22, or part-wind: ing sections, for any one pole of the field-winding 20, are all wound around the shank of the same pole-piece ll, so that these coils or partwinding sections 22 are concentric, that is, theyall have substantially a common center-line, as distinguished from the so-called distributedwinding arrangement in which successive coils.

are displaced slightly in space, by an amount equal to 180 electrical degrees divided bythe number of coils per pole.

The effect of the concentricity of all of the coils of any one polar-winding is that all of these coils, or part-winding sections, produce magnetic flux along approximately the same magnetic axis or center-line of the pole ll, the word approximately being utilized because, under the influence of armature-reaction, the flux is distorted or shifted somewhat from the exact vcenter-line of the pole, while still being confined well within the limits'of the pole-piece, as is well understood in the art. A further effect of the coaxial arrangement of the coils or part-winding sections of any pole is to cause these coils to have a rather high mutual inductance with respect to each other, because their magneticfluxes all traverse the same magnetic path; in-

this case the shank of the pole-piece ll.

Cooperating with the armature- The field-core carries a field-winding 20, arranged in- The foregoing represents the essential feature of my field-winding 2! namely that the serially connected part-winding sections 22 of each pole of the field-winding shall be substantially concentric, or shall be what isknown as a concentrated type of winding, rather than a distributed winding, and I desire my illustration of the preferred form of construction, in the salient-pole motor of Fig. 1, to be construed as representative; of any concentric-coil field-winding, whether mounted on a salient-pole field-core, or a smooth field-core;

The rotor-member or field-member I4 is also provided with. a multi-segment commutatormember 25, the successive segments of which are connected to-theAsuccessive electrical connections2 I, 23, and 24 of the serially connected coils 22-'of'the field-winding 20. The stator-member 8 carries, brush-rigging 25 for supporting a set of three-phase brushes 2'! which are disposed in contact-making engagement with the commutator-member 25, with phase-displacements of 120- electrical degrees therebetween.- The field-Winding 20 is connected to the--commu--- tater-member- '25 so thateach pole of thefield winding is connected across 180 electrical degrees of thecommutator-member; with. the successiveserially connected coils or part-windingsections 22 'connected'between successive segments of the commutator-member.

The resultoithe commutated field-Windingai rangement just described is that, Whenthe-.motor is operatingat a speedin synchronism with three-phase currents which are supplied to thethree brushes El, the flux-traversingthe-iield core lBi'l remains unidirectional, andsubstantial-ly non-pulsatory. Inother words, one

pole becomes a north pole, the next one a soutlr pole, and so on around the-"machinaior as many ,poles'as there are, and-the magnitude of the fluxes in these poles remains constant, so long asthe alternating-current input into the brushesis constant; This is'approximately true-even if the number of turnsineach of the coils or partwindingsectionsn of the field-winding 20 is the same-for all'of the -coils,-butthis condition is -morenearly appr-oached if the number 0! turnsof the coils orpart-winding sections 22 is reduced; or tapered off, for the coils which are closest to the pole-terminals 23 and 24 of the field-winding, that is, the pointswhere successive poles of the field-winding-are connected together: It will -be-noted that, to obtain this effect of a constantor-non-pulsatory unidirecpart-winding sections 22-of any pole-piece H are tional exciting fluxthe total number of coils or through them in a direction bucking the magnetization of the majorityof the coils. The relativemagnitudes of the three-phase currents, and

the time-phase relations between them, are such thatthe total effect is a constant unidirectionali flux for 'any given magnitude of alternating current, parti'cular ly if the numbers of turns oiithe coils are tapered down in the vic-inity;of"the pole-terminals 23'and M so that an approxi-' 'mately sinusoidal variation in the total or resultant 'fluxor ampere-turns would b obtained if direct current-Were passed between. any/two of the three brushes 21, while the commutator is rotating;

The magnitude of the unidirectional total or resultant magnetomotive force or ampere-turns in each .of the salient poles I'I depends upon the.

phase-position of the brushes 21 with respect to the phase of the alternating current which is fed into the brushes and thence to the field-winding 2|]. Thus, the field-excitation is a maximum when the brush of the phase which is carrying the maximum current, at the instant of currentmaximum in that phase, is resting upon the commutator-segment which is connected to the poleterminal, say 23, at that moment; and any departure from that position will result in a diminution in the magnitude of the total or resultant field-flux, approximately in accordance with the cosine of the electrical angle of the phase-shift of the brushes.

The normal no-load unity-power-factor position of the center-line 30 of the poles is in quadrature relation to the center-line of the rotating stator flux. At the moment of current-maximum of the current in any phase, such as the phase II, the flux-position of the rotating stator-flux is coincident with the center-line of that phase, and in Fig. 1 the rotor-member has been shown in the relative position which it would have, during synchronous operation, at such a moment, at unity power-factor andno-load. In the normal operation of synchronous motor, the rotor-position at the moment of current-maximum in the principal phase II will shift by a so-called loadangle which I can indicate as P, and also in accordance with the power-factor angle, which I can designateas Q, synchronous motors being usually operated overexcited, so as to produce a leading power factor, or so as to feed magnetiz ing wattless kva into the line.

In Fig. 1, I have shown the brushes 21 set back by an angle S, back of the position which would be in quadrature relation to the center-line of the phase-winding II, [2 or l3 to which the respective brushes ar connected. That is, if the motor is operating in a clockwise direction, as indicated by the arrow 3|, the brushes 21 are shown as being set back in a counterclockwise direction, by an angle S with respect to what I call the normal exciting axis 30, which is in quadrature relation to the phase which excites any particular brush 21. The total magnitude of the uni directional exciting-flux in each pole-piece [1, will, therefore, be proportional to the magnitude of the alternating current I, multiplied by the cosine of the angle (P-l-Q-S). Now S may be either zero, or plus, or minus, which is to say that each brush 21 may be set on its normal quadrature-related exciting-axis 30, or it may be set back by an angle S, as shown in Fig. 1, or it may beset ahead, in the other direction, by'an angle (S).

The adjustment of the angular phase-position or setting S of the brushes provides an instrumentality whereby the design-engineer or the user may predetermine the wattless characteristics of the motor, or the response of the motor to changing load-conditions. For instance, if the load should double, the load-current would approximately double, or materially increase, so that the resultant or total magnetomotive-force in the field-poles I! would approximately double, if it were not for the changing relative phasepositions. The doubling of the load approximately doubles the load-angle P, or causes it to increase, at any rate, so that the effective excitation-angle (P+Q-S) is also changed. The relation between the total field-magnetomotive- Iorceand the total field-flux is determinedbythe magnetizing curve of the machine, and an adjustment of the magnitude and direction of the brush-shift S gives the designer or the operator an opportunity to set the brushes so that the machine ordinarily offsets the tendency of a synchronous motor, which is operating at a leading power factor, to increase its power-factor, or decrease its magnetizing wattless kva, when the load increases; and it thus becomes possible to control the slope of the power-factor curve with respect to changing loads, or the slope of the.

wattless-kva curve with changing loads, making this curve either approximately flat, or sloping either up or down, as may be required or desired. In other words, a control of the brush-shaft angle S, in my new design of motor, makes it possible to give the motor, within certain limits, a predetermined inherent wattless or power-factor characteristic, with changing motor-loads.

My improved motor, as shown in Fig. l, is started by the simple expedient of closing a line switch or breaker 33. The motor then starts, very much after the manner of a three-phase commutator-motor except that the rotor of my motor produces only a pulsating flux, in a fixed magnetic axis with respect to the rotor-position, instead of a rotating magnetic flux which can rotate in all positions around the rotor, not being fixed by the rotor-position. My pulsating alternating flux, which is obtained during the starting-conditions, is resolvable into forwardly and backwardly rotating components, each of half of the magnitude of the total pulsating flux. The starting-torque equations are quite complicated, .but the principal starting torque is obtained from the coaction between the rotating stator-field and the correspondingly or forwardly rotating component of the rotor-field, and these two fields, reacting together, produce a strong starting torque, for any given field-magnitude. My motor is thus able to develop a larger starting-torque, on a smaller starting-current inrush, than is possible in the ordinary synchronous motor which starts on damper windings after the manner of a squirrel-cage inductionmotor. In my motor, no damper windings are utilized at all.

The starting characteristics of my motor are also affected by the brush-positioning S, and by the reactance of the field-winding, particularly at the moment of starting. It is well known that a polyphase commutator motor develops a starting-torque dependent upon the amount by which the brushes are shifted from their position of coincidence with the phase-axis, or the angle (S), measuring S from the quadrature-related position 30, as indicated in Fig. l. justment of the brush-shift angle S, or a preselection of the brush-shift angle S, constitutes a means which is available to the operator or to the designer, in adapting the motor for desirable starting-characteristics.

' The reactance of my commutated field-winding 20 is a valuable starting-asset, particularly to the series-excited motor which has been described in connection with Fig. 1. It has already been pointed out that, at synchronous speed, the flux through the field-core |'6-.i I does not change with the 60-cycle or line-frequency alternations of the current, but remains fixed and constant, for any given magnitude of current and relative phase-position of the rotor. Under these synchronous-speed conditions, therefore, the steady-state value of the field-flux cooperates with the strong mutual inductance between the An adrush, making it possibleto start the motor, even on the full line-voltage, without-an excessive:cur rent-inrush, in many instances:

The concentric-coil I arrangement of: myl-com' mutated polyphase-excited r field-winding: 201 causes my motor, whentit reaches synchronousl speed, during the starting operation,-to =autoflmatically and quietly drop into step, withoutiany disturbance on the supply-line 'andwith-outany attention whatsoever from the operator: If'zit' were not for the characteristic of my motor-which gixes it a fixed field-flux axis (fixed with respect: to the rotor), my motor would'nothesitate at the synchronous speed but would passrightthrough synchronism, as in any other? polypha'se synchronous machine- My fixed field-excitation axis, coupled with the characteristic nethe -ma chine to develop a unidirectional magnetomotiv'e' force proportional to the alternating -currentmagnitude multiplied by the cosine of the angle (P-l-QS) gives my motor a strongpu ='-ir itorque and a strong pull-out torque; which=en ables it to operate as a synchronous motor, while:- at the same time giving the-motor very-superio rinherent power-factor regulation in regard to'the wattless-kva characteristic.

While I have thus far describedr'lmymotomin detail, with respect to a series-excited three* phase embodiment, asshown in Fig. 1i myinvention is not limited to this'particular em-b'oclin'ient, and my machine may be utilized as' -a generator; as wellas a motor.

In Fig. 2, I have illustrated a* synchronous machine in which the rotor-member is n'ot"ex-'- cited in series-circuit relation to the stator-mem her, but in shunt-circuit relation th'eretov- As in all commutator motors, it is desirableto limit the magnitudes of the voltages appearing iri the coils undergoing commutation.- lt -is usual-ly dee sirable to design the field-Winding-\VhiCh iS c0fi nected to the commutator for' alowerrvoltage than the fuil line-voltage, andtI:haveiaccordmgly indicated this feature in Fig. 2 by showingsmstefi down three-phase transformer 3'1 for'energizlng the brushes 2? from the three-phase suppiyi linez In Fig. 2, I have also illustrateduthe:brusheposr tion, as indicated by the line 38;in:quadrature re-: lation to the axis 39 of the statoite'win'din'g which is connected to the samelineephase a'sztheibrusht in other words, I have illustrated thexbrush-di'sr-t placement angle S as being:;zero;. In"ot=her::re -r spects, the motor illustratedin='Fig. 2 is, orfmay be, similar to that which'isshown ina-Fig.=.,1.

In Fig. 3, I have illustratedmyinvention asebe-i ing applied to a single phase moton-lhavingra serially connected, single phase' excited,.commu field-coilswor field win'ding sectlonxto the? tat'ed lrotor or fieldi-memberii. Inithis iorm of my invention", I utilize only! two brushes 21 .WhiChl are v connected: in 1 series with the main stator winding H across? a single=phase supply lineasuch a' single-phase motort'will preferably have;

some sort 10f ssplit phase or other means for pro duoingsa rotatingrstator torque; astbyi means-of aniauxiliary statorewiridihgd M 'in space=quadra ture' relatiemzto theimain stator-winding! I; the auxiliaryzstatofiwinding: M :ha'vingdephased cur rents? therein, such: as: might be produced by" a'-* serlafllyl" connected: capacitor 4-2; the auxiliary winding! I 5 withitsfcapacitor' 42 being en'ergized across: the "sin'gle-phase supply-dine.

While'I have illustrated my: invention in sever a] different forms of embodimentcand'while I: have' explainedi the' principlesv thereof :in accordance with my be'stpresent understanding of the sameg-l wish it to-"be' understoodv that'I am'not' limited,- eith'er to the'precise forms of embodiment:

of myiinventlomor as to everyi'detall-of the prin-- ciples and t-theo-ries which have been-referred to in attemptingto explain'its operation' and advan tage's. I consider that :myxbasic invention consist'sdn the broad idea'iof utilizing a commutatedfield-winding; with line-frequency. excitation, orexcitatl'on' :byany-alternating currents which aresynchronized with the "line frequency, and with'a plurality of concentric field-coils or field-winding;

, sectl'ons foriieach:polef'of the field-winding. I desire, therefore, that'the-broadest of the appended claimsl'shall-be broadly; construed: as being: directed toithisi basic invention; withoutlimitation to structuraldetai'l's or'theoriesof design oroper I claim as my invention:

1. synchronous dynamo-electric machine comprisingan armaturememberand a; field member; onerotatable relatively to the other. in dynamo-electric "relation, said armature member having a p-p'olearmature w-inding; said fieldmember havir'igarr-pole field-winding; where-p-is an" even number; eachpol'e of the 'field windin'gr comprising a plurality-- of concentric mutually inductiVepart-Windirig sections "all havingasubstanti'a'lly common center-"line; thepart-winding sections of 'eachpair'- ofpolsbeing serially-related insuch polarity' thatone pole has one po'-' larityancl the other pole hasthe' opposite polarity, a multi-segment commutator-member carried by the field. member, commutatonconnections for connecting successive serially-connected part winding sections of the" field windin'g' between successive segments of the commutator-#membe'r, a plurality ofbrushescarried'by the'a'rmatur'e member in contact-making engagement with the commutator-member, and means for energizing said brushes with alternatingv current in syn ch'ronized relation to the 'arm'aturewin'ding current.-

2-A synchronous dynamo-electric ,machine comprising-an armature member and a field mem' ber, one-rotatable-relatively to'th'e othrin dyna Ind-electric relation, said armaturemember'hav ing ap-pole armature-winding,.saidfield"membei havingga pepole field-winding,- where pis an evennumber, each-pole of the fieldiwindingicomprising a plurality-of concentric mutually inductive part-winding sections-all. having a substantially common center-line, the part-winding sectionsofeach pair of poles-being-.-serially related in such polarity; that one pole has r on polarity and' th eother pole 'has the: opposite polarity; -a multi segment commutator-member carried by the field member, commutator-connections for connecting successive serially-connected partwinding sections of the field-winding between successive segments of the commutator-member, a plurality of brushes carried by the armature member in contact-making engagement with the commutator-member, and means for energizing said brushes with alternating current in seriescircuit relation to the armature winding.

3. A synchronous dynamo-electric machine comprising an armature member and a field member, one rotatable relatively to the other in dynamo-electric relation, said armature member hav ing a p-pole armature-winding, said field member having a p-pole field-winding, where p is an even number, each pole of the field-winding comprising a plurality of concentric mutually inductive part-winding sections all having a substantially common center-line, the part-winding sections of each pair of poles being serially related in such polarity that one pole has one polarity and the other pole has the opposite polarity, a multi-segment commutator-member carried by the field member, commutator-connections for connecting successive serially-connected part-winding sections of the field-winding between successive segments of the commutatormember, a plurality of brushes carried by the armature member in contact-making engagement with the commutator-member, and means for energizing said brushes with alternating current in shunt-circuit relation to the armature-winding.

4. A synchronous dynamo-electric machine comprising an armature member and a field 1116111;

ber, one rotatable relatively to the other in dynamo-electric relation, said armature member having a p-pole n-phase polyphase armature-winding, said field member having a p-pole field-winding, where p is an even number, each pole of the field-winding comprising a plurality of concentric, mutually inductive part-winding sections all having a substantially common center-line, the part-winding sections of each pair of poles being serially related in such polarity that one pole has one polarity and the other'pole'has the opposite polarity, a multi-segment commutatormember carried by the field member, commutator-connections for connecting successive serially connected part-winding sections of the fieldwinding between successive segments of the commutator-member, n-phase-related brushes carried by the armature member in contact-making engagement with the commutator-member, and

means for energizing said brushes with polyphase current in synchronized relation to the armaturewinding current.

5. A synchronous dynamo-electric machine comprising an armature member and a field member, one rotatable relatively to the other in dynamo-electric relation, said armature member having a p-pole n-phase polyphase armature-winding, said field member having a p-pole field-winding, where p is an even number, each pole of the field-winding comprising a plurality of concentric, mutually inductive part-winding sections all having a substantially common center-line, the partwinding sections of each pair of poles being serially related in such polarity that one pole has one polarity and the other pole has the opposite polarity, a multi-segment commutator-member carried by the field member, commutator-connections for connecting successive serially connected part-winding sections of the field-winding between successive segments of the commutatormember, 'n-phase-related brushes carried by the armature member in contact-making engagement with the commutator-member, and means for energizing said brushes with polyphase current in series-circuit relation to the armaturewinding.

6. A synchronous dynamo-electric machine comprising an armature member and a field member, one rotatable relatively to the other in dynamo-electric relation, said armature member having a p-pole n-phase polyphase armature-winding, said field member having a p pole field-winding, where p is an even number, each pole of the field-winding comprising a plurality of concentric, mutually inductive part-winding sections all having a substantially common center-line, the partwinding sections of each pair of poles being serially related in such polarity that one pole has one polarity and the other pole has the opposite polarity, a multi-segment commutator-member carried by the field member, commutator-connections for connecting successive serially connected part-winding sections of the field-winding between successive segments of the commutatormember, n-phase-related brushes carried by the armature member in contact-making engagement with the commutator-member, and means for energizing said brushes with polyphase current in shunt-circuit relation to the armature-winding.

7. A self-excited synchronous machine comprising a stator-member having an nphase polyphase armature-winding, a rotor-member having a field-winding producing alternate north and south poles, each pole of the field-winding comprising a plurality of concentric part-winding sections all having a substantially common center-line, the part-Winding sections of each pair of poles being serially related, said rotor-member also including a multi-segment commutatormember having n-phase-related brushes bearing thereon, commutator-connections for connecting each pole of the field-winding across 180 electrical degrees of the commutator-member, with successive serially connected part-Winding sections of the field-Winding connected between successive segments of the commutator-member, and

means including brush-connections for energizing the brushes in a predetermined manner from the polyphase armature winding.

8. A self-excited synchronous machine comprising a stator-member having a polyphase armature-winding having two sets of three-phase terminals, a rotor-member having a field-winding producing alternate north and south poles, each pole of the field-winding comprising a plurality of concentric part-winding sections all having a substantially common center-line, the part-winding sections of each pair of poles being serially related, said rotor-member also including a multi-segment commutator-member having brushes bearing thereon with phase-displacements of electrical degrees therebetween, commutator-connections for connecting each pole of the field-winding across electrical degrees of the commutator-member, with successive serially connected part-winding sections of the field-winding connected between successive se ments of the commutator-member, and armature-connections for connecting one set of the armature-winding terminals to said brushes.

9. A self-excited synchronous machine comprising a stator-member having an armaturewinding of a type adapted to produce a rotating flux, a salient-pole rotor-member having fieldwindings on the salient pole-pieces, each pole of the field-windings comprisinga plurality of serially connected part-winding sections having elec- 'trical tap-conneritions between the sections; I said rotor-member also including a multi-segment commutator-member having a plurality -of i i a "predetermined manner= from the armawre winding.

10. .A self-excited synchronousma-chine comprising a stator-membevhaVing a polyphase armature-winding; a salient pole rotor-member having field windings on the salient'p'ole pieces,

each pole of the" field-findings comprisingaplur'ality of serially connectedpart winding sections having. electrical 'tap=connections--- between the sections, 's'a'id rotor member -also 'including a multi segment commutator -'mcmbe1 having .three phase-related brushes bearing thereon,

commutator-connections for connecting each pole 'of thefield-winriing across "lfiflelectrical degrees .of 'the .commutator-member;with successive serially connected part-winding sections of the field-winding connected between 'successivesegments ofythe commutator member," and means :including brush-connections for energizing the three phase r'elated v brushes with three-phase currents obtained in a" predetermined 'manner from the p'olyphase armature-Winding. I 11 A self-starting self-excited synchronous machine comprising a stator-member having a laminated armature-core and a polyphase armature-winding carried"bysaidarmature-core, a

rotor-member having afield-core and a field winding carried by said field-core; at least the portion of the field-core which: carriesthe fieldwinding being'laminated, said field-winding producing alternate north and, soutlrpolesdnring synchronous operation; each'p'ole of the .field-' winding comprising a plurality of concentric part-winding sections all having a substantially common center-line, the part -winding sectionsiof eachpair of poles-being serially related, said rotor-member also including a multi-segment commutatonmember having polyphase-related brushes bearing thereon, commutator-connections forconnecting each pole of the fie'ld wind- "ing across 180 electrical degrees of the commutator-member; with successive serially connected part-w'md-ing sectionsof the field-Winding connected between successive segments of the commutator-member, and means for energizing said polyphase-r elated brushes with polyphase current "inseries-circuit relation to the polyphase armatum-winding.

- 12.' The invention as defined in claim 2, characterized'by said brushesbeing displaced from aposition in quadraturerelation to the armaturewinding by an amount such as to give the machines. desired wattless kva characteristic under predetermined variable load-conditions and over a predetermined *range of wattless kva.

f 1.3."The invention as defined in claim 5, characterized by said brushes being displaced from a positionin-quadrature relation to the armature winding byan' amount such as to give the machine adesired wattless-kva characteristic under predetermined variable load-conditions and over a predetermined range of Wattless kva.

4 14; The invention asdefined in claim 8, characterized by said'brushesbeing-displaced from a -p0sition'in quadrature relation to the armature-Winding by an amount such as to g'ivethe machine a desired wattless kva characteristic under predetermined variable load-conditions and overa' predetermined range of wattless'kva.

' l5 Theinvention as defined in claim 11, characterized by said brushesbeing displaced from a position-in quadrature relation to'the armature-Windingjby an amount'such' as to give the 'machine-a desired wattless kva characteristic under-predetermined variable load-conditions and over apredetermined range ofwattless kva, and to give the' 'machine' a desired starting characteristic.

ROBERT" C. ROBINSON. 

